During wafer fabrication, the deposition formation rate and etching removal rate depend on the input flow rate and the chamber pressure of the process gases. Changes in input flows create changes in chamber pressure; but, these changes do not directly correlate with changes in the deposited layer in a deposition system or to material removal in an etch system during a given exposure time.
Heretofore, the determination of the process gas input flow rate was based on a best measurement of the ambient temperature of the reaction chamber, and a best estimate of the volume of the chamber at that ambient temperature. The measured temperature required an absolute baseline temperature determined through calibrated instruments. This baseline temperature was only as accurate as the instrument quality and condition, and the effectiveness of the calibration technique. Further, raising the reaction chamber to the operating temperature introduced a basic transition error.